Slowdown control for reversing hot mill



June 9, 1964 c. R. DART SLOWDOWN CONTROL. FOR REVERSING HOT MILL 4 Sheets-Sheet 1 Filed Aug. 29, 1961 TUE mEzaou 028%. T

$525 mEmZ/EFLQ KmPZDOU .rwmE

ON mJOEpZOU 1| I I I I I 02 $1 INVENTOR. CHARLES R.DART

ATTORNEY June 9, 1964 c. R. DART SLOWDOWN CONTROL FOR REVERSING HOT MILL Filed Aug. 29. 1961 T XE-JJI'I 4 Sheets-Sheet 2 FIG.

PUL$E RATE ADJUSTOR FIG. FIG. 2A 2 B FIGZA CCNT RESET TACHOM ETER FIG.2

June 9, 1964 c. R. DART SLOWDOWN CONTROL FOR REVERSING HOT MILL 4 Sheets-Sheet 3 Filed Aug. 29, 1961 June 9, 1964 c. R. DART 3,136,183

SLOWDOWN CONTROL FOR REVERSING HOT MILL Filed Aug. 29, 1961 4 Sheets-Sheet 4 BOLVDICINI G33dS SLOWDOWN United States Patent 3,136,183 SLOWDOWN CONTROL FUR REVERSING HOT MILL Charles R. Dart, Roanoke, Va., assignor to General Electric Company, a corporation of New York Filed Aug. 29, 1961, Ser. No. 134,778 8 Claims. (Cl. Sit-$3) This invention relates to an automatic slowdown control for a reversing hot mill.

In reversing hot mills the hot metal being rolled is first fed through the one set of rolls in one direction, the rolls are then reversed and the hot metal is fed through the reversed rolls. This is repeated until the metal has been reduced to the desired thickness.

The hot metal while being rolled travels at a high rate of speed and if the tail end of the metalleaves the rolls at such high speeds the tail end comes to rest a considerable distance from the rolls. The farther from the rolls the tail end comes to rest the longer it takes to return the hot metal to the rolls for the return trip through the rolls. It has, therefore, been the practice to slowdown the rolls before the tail end leaves the rolls so that the tail end of the hot metal leaves the rolls at a slow speed and comes to rest a short'distance from the rolls. After the rolls are reversed, it, therefore,-requires only a short period of time to return the tail end of the hot metal to the rolls. a

It is, therefore, an object of this invention to provide a control for slowing down the hot metal in a reversing hot mill before the tail end of the hot metal leaves-the rolls.

Heretofore, hot metal detectors have been utilized, in

slowing down the hot metal. The hot metal detector would detect when the tail end of the hot metal passes a certain point and slow down the hot metal before it leaves the rolls. 1

Hot metal travels at various speeds depending on the operation being performed; and the faster the hot metal is traveling, the farther from the rolls the slowdown must be initiated. It is not economically practical to initiate the slowdown for theslower speeds at the same point the slowdown is initiated for the faster speeds.

It is, therefore, another object of this'invention to provide a slowdown control for a reversing hot mill capa-.

ble of slowing down the hot metal when the tail end of the metal-is at different distances from the rolls depending on the speed at which the hot metal is traveling.

Selecting the slowdown point'depending on the speed .of the metal enables all hot metals to continue at high speed until it is neecssary to slow them down so that the tail end leaves the rolls'at a slow speed. In the past this problem has been partially solved by providing two or three hot metal detectors on each side of the mill. at different distances from the rolls. The detector selected depends on the speed at which the metal is traveling. The farthest detector from the rolls is selected for the fastest speed and the closest detector for the slowest speed. However, hot metal detectors are expensive. It has not been economically feasible to provide a pair of hot metal detectors for each speed of the hot metal, and the slowdown has not been as accurate as is desirable. In the past, each pair of hot metal detectors has functioned for more than one'speed ofthe hot metal.

An' object of this invention, therefore, is to provide a new and improved slowdown control for a reversing hot mill capable of more accurate slowdown control than previous apparatus used. Another object is to providea more economical slowdown control.

This invention provides a new and improved slowdown control for a reversing hot mill. Whenthe hot metal enters the rolls, pulses from a tachometer connected to the motor driving the rolls are delivered to a first counter. As the hot metal travels through the rolls, the counter counts the pulses; and when the tail end of the metal leaves the rolls, a number representing the length of the metal which has traveled through the rolls rests in the counter. This number is transferred to a second counter, the rolls are reversed, and the tail end of the metal is fed into the rolls for a return trip through the rolls. The number in the second counter is reduced as the metal travels through the rolls; and when the number is reduced to a number representing the. remaining length of the hot metal when slowdown should be initiated, a signal is produced to initiate slowdown. However, each time the hot metal completes a trip through the rolls the thickness is decreased, the length is increased, and the number transferred" to the second counter does not represent the length of the hot metal after the second pass through the rolls. j Compensation is made by adjusting the number in the second counter afterthe transfer of the number to the second counter'in accordance with the decrease in thickness and resulting increase in length.

For each speed at which the hot metal is traveling a specific number in the second counter is examined; and when the second counter has been reduced to thatnum ber, slowdown of the'hot metal is initiated.

The slowdown control embodying this invention provides an accurate control for initiating slowdown of a hot metal before the tail end leaves the rolls. The hot metal may be slowed down at different distances from therolls' depending on the speed of the hot metal. The

' slowdown control is economical and replaces a plurality of hot metal detectors.

The novel features of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together withfurther objects and advantages thereof, may best be understood by referring to the fol: lowing description and the accompanying drawings.

In the figures:

FIG. 1 is a block diagram of a slowdown control constructed in accordance with the principles of this invention. i I

FIG. 2 is a diagram showing how to assemble FIGS.

2A, 2B, and 20 when assembled as shown in FIG. 2

show a schematic'of the block diagram shown inFIG. 1.

In the figures certain conventions are used as follows: A conventional filled-in arrowhead is employed on lines to indicate (1) a circuit connection, (2) energiz'ation with standard negative pulses, and (3) the direction of pulse travel which is also the direction of control. A filled-in diamond-shaped arrowhead indicates (l) a circuit connection and (2) energization with a negative D.C. level.

In the description, the general arrangement of the apparatus and general over-all operation of this apparatus will be described first. The various apparatus which require a detailed description will be described later in the description.

Reference should first be made to FIG. 1 for a general description of the slowdown control of a hot reversing mill. The operation of a reversing hot mill will first be described.

A hot metal 9 is fed in the direction shown between a top roll 11 rotating in a counterclockwise direction and a bottom roll 13 rotating in a clockwise direction. Rolls 11 and 13 are rotated by a motor shown with its controls as a block 14 connected by dashed lines to the rolls 11 and 13. A metal in rolls detector 15 may be a hot metal detector to detect the presence of the hot metal between the rolls 11 and 13. After passing through the rolls 11 and 13 the thickness of the hot metal 9 is decreased. After the entire hot metal has passed through the rolls 11 and 13, the metal in rolls detector 15 detects the lack of a hot metal in the rolls 11 and 13 and so signals the reverse control 16. The reverse control 16 then delivers a signal to the motor and controls 14 which reverse the direction of rotation of the rolls 11 and 13 and the hot metal 9 is returned to the rolls for another run through the rolls in the reverse direction. The general operation of a reversing hot mill is well known and will not be further described here.

Still referring to FIG. 1-the general operation of the slowdown control will be described. As the hot metal is fed into the rolls, the metal in rolls detector 15 detects that fact and activates the slowdown 'control'by several actions. The first counter 17, the second counter 18, and the rate adjuster 19 are reset to zero. Gates and 21 are conditioned to pass pulses.

' Tachometer 24 measures the velocity of the shaft of the motor 14 and generates pulses directly related to the length of the hot metal passed through rolls 11 and 13 and the pulses are applied to gate 20 and rate adjuster 19. Gate 20 is conditioned to pass the pulses generated by the tachometer 24 to the first counter 17. The first counter 17 counts the pulses generated by tachometer 24 so long as the metal 9 is passing between rolls 11 and 13.

The pulses applied to rate adjuster 19 are adjusted in a manner to be described and applied to the second counter 18 through conditioned gate 21, to effect an operation which will be described later.

On the first pass through the rolls the metal 9 is not slowed down before it leaves the rolls. As soon as the metal 9 leaves the rolls, the absence of the metal is detected by the metal in rolls detector 15 and gates 20 and 21 are deconditioned and no further pulses are passed by the gates 20 and 21 and applied to the counters.

The number accumulated in the first counter represents the length of the hot metal which has passed through the rolls 11 and 13.

After the hot metal leaves the rolls second counter 18 and rate adjuster 19 are cleared.

The metal in rolls detector 15 delivers a signal to the reverse circuit 16 indicating that the metal 9 has left the rolls and that the rolls are to be reversed for the reverse run of the metal 9 through the rolls 11 and 13. Reverse circuit 16 delivers a signal to the motor and controls 14 causing the motor to reverse the direction of rotation of the rolls 11 and 13. The reverse circuit 16 also delivers a signal to the transfer circuits causing the number in the first counter 17 to be transferred to the second counter 18. The first counter 17 is then cleared.

The number now resting in the second counter 18 represents the length of the hot metal which has passed through the rolls 11 and 13. c

The metal 9 is then introduced again into the rolls 11 and 13 for the reverse run through the rolls. The metal in rolls detector 15 detects the presence of the hot metal 9 and conditions gates 20 and 21. The tachometer 24 again generates pulses which are applied through V the rolls 11 and 13, the number in the second counter 18 is decreased accordingly.

The motor 14 operates at dilferent speeds moving the metal 9 at different speeds and the slowdown of the hot metal must be initiated at a different distance from the rolls for each different speed of travel of the metal 9. The speed at which the motor is moving the metal is determined by the controls of the motor and indicated in the speed indicator 22. The speed indicator 22 delivers signals to comparison circuit 23 indicating when the slowdown of the metal 9 should be initiated.

A comparison is made between the signals delivered from the speed indicator 22 and the number in the second counter; and when a comparison is effected, indicating an equality between the number from the speed indicator 22 and the number in the second counter, a signal is delivered to the slowdown control 26 which in turn delivers a signal to the motor and controls 14 to initiate a slowdown of the motor and the hot metal 9.

However, the thickness of the metal is reduced after each pass through the rolls 11 and 13 and the length of the metal is increased. Therefore, the number transferred to the second counter 18 represents the length of the metal which has just been rolled and not the length of the metal after the next pass and which is to be slowed down before its end leaves the rolls.

Compensation is, therefore, made for the decrease in thickness and resulting increase in length by entering into the thickness compensator 27 a representation of the change in thickness which is to be effected by a pass through the rolls. The decrease in thickness caused by the run through the rolls is known and the length increases a predetermined factor for each decrease in thickness. This length compensating factor is entered into the rate adjuster 19 from the thickness compensator 27.

For a better understanding of the need for the thickness compensation factor, assume that the metal has passed through the rolls and that the first counter 17 has counted to 1000 so that the length of the metal is represented by the number 1000. Further, assume that as the metal passes through the rolls on its return trip, the thickness will be reduced X percent; and for such a thickness decrease, it is known that the length will be increased 20% so that the length of the metal after the reverse run through the rolls will be represented by the number 1200. Thus, when the number 1 0 00 is transferred to the second counter before the reverse run through the rolls, the number 1000 represents the length of the metal just rolled, not the length of the metal after the next pass. Further, assume for the specific speed at which the metal is being rolled, it is necessary toinitiate the slowdown a distance from the rolls represented by the number 20. As stated the pulses applied to the second counter 18 reduce the number stored therein. Thus, if the slowdown were initiated when the number 1000 was reduced to the number 20, the metal would still have a length represented by the number 220 which had not passed through the rolls. The thickness compensation factor compensates for the increase in length in a manner to be described.

The pulses generated by tachometer 24 are applied to rate adjustor 19. 'The thickness compensation factor is entered into thickness compensator 24 and the appropriate length compensation factor is transferred to the rate adjustor 19. In the example given the thickness reduction of percent X resulted in a length increase of 2 0% sothat the length after the first passwas repre.-

counter bit to change states.

sented by the number 1000 and after the reverse pass the length would be represented by the number 1200." The number resting in the second counter 18 is 1000 and the slowdown is to be initiated when the second counter has been reduced to the number 20. The length compensation factor causes the rate adjustor 19 to inhibit 16.7% of the pulses generated by the tachometer-24 so, that only 83.3% of the pulses generated are delivered to the second counter. Thus, for every 1.2 pulses applied to the rate adjustor 19 only 1 pulse is delivered to the second counter, and the number 1000 in the second counter 18 is reduced accordingly. The number l000 is reduced effectively as if it were the number 1200. Thus, when the number 1000 is reduced to the number 20, a comparison is made in the comparison circuit 23 with the signals in the speed indicator 22 and a signal is delivered to the slowdown circuit 26 to initiate slowdown in the motor and controls 14. It should be noted that the number 20 represents a length equal to 24 in the length of the metal after the second pass.

The hot metal 9 leaves the rolls at reduced speed and comes to rest a short distance from the rolls. The metal in rolls detector detects the absence of the metal in the rolls, deconditions gates and 21, and signals the reverse circuit 16 to prepare for another run through the rolls in a reverse direction.

The reverse circuit causes the motor and controls 14 to reverse the direction of rotation of the rolls 11 and 13. The rate adjustor 19 and second counter 18 are cleared.

The number in the first counter 17 is transferred through repeated.

RATE ADJUSTMENT CIRCUIT The rate adjustment circuit shown as block 19 in FIG.

1 is shown in more detail in FIG. 2A. The circuit is composed of seven counter bits 40-46, associated capacitors 50-56, diodes 60-66, and associated circuitry. Cir-.

cuit wires 70, 71 and 76 are connected from points $0,-

81, and 86, through resistors 90, 91, and 96 to ground.

Circuit wires 72-75 are connected from points 82-85,- U

f shown in step 2 represents a decimal number of 2 as is through resistors 92-95, to either ground or a negative potential inamanner to be described.

Each counter bit 40-46 used in the rate adjustment circuit is internally connected in such a way that a signal applied to the terminal labeled IN will cause the tive D.C. level is delivered on the terminal labeled 1, and the terminal labeled 0 is at ground potential. In

the Zero state a negative D.C. level is delivered on the terminal labeled 0 and the terminallabeled 1is at ground potential. The 1 and 0 terminals are always the inverse of'each other. The shift of the output signal from terminal 0 to terminal 1 of a counter bit and vice versa occurs on the positive going side of the input signal. The counter bit may be reset to the zero state by a signal on the terminal labeled RST.

. Counter bits 40-46 are connected to function as a binary counter. Binary counters are well known in the art and the general arithmetic operation of binary counters will not be explained here except as it uniquely applies to this binary counter. Referring now to Table 1, all counter bits 40-46 are reset to the zero state with the 1 terminal at ground potential and the 0 terminals delivering a negative signal. Pulses are applied to the input terminal of counter bit 40 from tachometer 24. The first pulse from the tachometer 24 on its positive going side causes counter hit 40 to change to the one state as shown in step 1 of Table 1 and to deliver a negative signal on the 1 terminal.

In the one state a nega- Table 1' ter bit 40 changes state again and the negative output level from the 1 terminal of counter bit 40 goes to ground potential as counter bits 40-46 change states on the positive going side of the applied signal.

The second pulse from the tachometer 24 applied to the input terminal of counter bit 40 causes counter bit 40 to change from the one to the zero state with the negative output level applied to the input terminal of counter bit 41 going from a negative signal to ground potential. Counter bit 41 then changes to the one state, with a negative output signal delivered from its 1 terminal to the input terminal of counter bit 42. After the application of the second pulse, counter bit 40 is in the zero state and counter bit 41 is in the one state as shown in step 2 of Table 1. The binary number, 0100000 and to count the pulses from the tachometer 24 inbinary form in the manner described. Table 1 shows the binary number in counter bits 40-46 resulting from pulses 1-24, 42-43, and 71-72, assuming that the pulses not represented have also been applied to counter bit 40.

.- The counter portion of pulse rate adjustment circuit hasbeen described as a counter. As described in the functional description of the pulse rates adjustment circuit 19, the function of the circuit is to v apply pulses at a slower rate to the second counter to compensate for the thickness decrease and resulting length increase in the metal being rolled. Thenumber in the second counter is decreased at a slower rate than the same number was increased when it was in the first counter. The pulses from the tachometer are applied to the pulse rate adjustment circuit and in response, thereto, pulses are produced at a controlled rate dilferent from the rate received'in a manner to be terminal is at ground potential. The next pulse applied to counter bit 40 causes counter bit 40 to change to the zero state and the 0 terminal to deliver a negative signal. A potential difference thus exists between the 0 terminal and ground; and capacitor 50 is charged to a negative voltage, then discharges, delivering a pulse through gate 21 when conditioned to the second counter. A pulse is thus delivered from the pulse rate adjuster when a counter bit changes from the one state to the zero state and the respective circuit wire 7 0-76connects a point 80-86 to ground potential. The production of a pulse from a counter bit is indicated in Table 1 by an X. By examination it can be seen that counter bit 40 produces one pulse for every two pulses received from the tachometer, counter bit 41 produces one pulse for every four pulses received, counter bit 42 produces one pulse for every eight pulses, and counter bit 43 produces one pulse for every 16 pulses. Further, counter hit 44 produces one pulsefor every 32 pulses received, bit 45 produces one pulse for every 64 pulses, and bit 46 produces one pulse for every 128 pulses received. Thus, normally for every 128 pulses received 127 pulses are produced.

The pulse production adjustment will now be described. In the particular embodiment described the only compensation made is for the change in thickness resulting in increased length.

The data indicating the decrease in thickness is entered Table 2 Counter Number of Number of Lines bits ulses pulses proinhibited inhibited duced for 128 received For the purposes of the immediate description, assume that a negative signal is delivered on line 101 through OR circuit 107, through resistor 92 to point 82, so that point 82 is at a negative potential. Therefore, when counter bit 42 changes from the one to the zero state and delivers a negative signal in the 0 terminal, no potential difference exists between the 0 terminal and point 82. Capacitor 52. is, therefore, not charged and no pulse is delivered from the pulse rate adjustor. Referring to Table 2, it can be seen that normally counter bit 42 produces one pulse for every eight pulses applied. Table 2 tabulates the number of pulses inhibited and produced for the combination of counter bits inhibited for 128 pulses received by the pulse rate adjustor. Thus, when counter hit 42 is inhibited by the application of a negative signal from line 101, the pulse rate adjustor produces only 111 pulses for every 128 pulses applied.

The inhibition of additional pulses may be accomplished in a similar manner by applying negative signals on other lines to inhibit other combinations of counter bits.

Table 3 Decimal value 1 2 4 8 16 32 64 128 256 512 1024 2048 4096 Counter bit 1 2 3 4 5 6 7 8 9 10 11 12 13- First counter:

0 0 0 0 0 0 0 0 O 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 (1 0 1 O 0 0 0 '0 0 0 O 0 0 0 l 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 r 0 0 0 0 0 0 0 0 1 1 0 1 0 1 1 0 1 1 1 0 1 0 0 1 1 0 1 1 0 1 1 1 O 1 1 0 1 1 0 1 1 0 1 1 1 0 1 0 1 1 1 0 1 1 O 1 1 1 O 1 1 1 1 1 0 1 1 O 1 1 l 0 1 0 0 O 0 1 1 1 0 1 1 1 0 1 Table 4 0 0 0 1 1 1 0 1 1 1 0 1 1 l 1 0 1 1 0 1 1 1 0 1 1 1 1 0 1 1 0 1 1 .1 0 l 0 1 1 0 1 1 0 1 1 1 O 1 0 1 l O 1 1 O 1 1 1 0 l 1 0 1 0 1 1 0 1 1 1 0 1 draft compensator in binary form and deliver a negative signal on one or more of the lines 100-106. Normally all of the lines 100-106 are at ground potential. For a description and discussion of suitable diode decoders see DETAILED DESCRIPTION OF THE FIRST AND SECOND COUNTER The first counter shown as block 17 in FIG. 1 is The Decoding Circuit, pages 547-552, in Ledley, Digital shown in more detail in FIGS. 2B and 2C. The first dounter is composed of thirteen counter bits 111-123 and operates as a binary counter in a manner similar to the rate adjustor shown in FIG. 2A. Referring to FIGS. 2B and 2C and Table 3, all counter bits 111-123 are first cleared to the zero state so that a negative signal is delivered from the 0 terminal of each one and all of the 1 terminals are at ground potential. This is represented by step 0 in Table 3. The first pulse applied to the first counter hit 111 causes the bit to change to the one state with a negative signal delivered to the 1 terminal as shown in step 1 of Table 3. The

next pulse applied to the first counter hit 111 causes the first counter bit 111 to change to the zero state and the shown in step 2 of Table 3. This represents the number2 in decimal form.

Subsequent pulses applied to the first'coun-ter from the tachometer 24 are counted in the counter in binary form until the hot metal 9 leaves the rolls and the number accumulated represents the length of the hot metal passed through the rolls. Step 5980 shows the binary representation for the decimal number 5980. The metal in rolls detector 15 activates the reverse circuit 16 and the reverse circuit 16 causes a transfer of the number transfer circuits 131-143 in a manner to be described.

Each of the And-Not circuits 131-143 produce an output signal when ground potential is applied to both inputs and produce no signal when a negative signal is "applied to either input. They are also known as Inverterber in the first counter to the second counter, the reverse circuit 16 applies ground potential to one terminal of each of the And-Not circuits 131-143. The

"counter bits in the first counter that are set to the one "state have their zero terminals at ground potential and 'no negative signal isdelivered to the corresponding And- Not circuit. Therefore, those And-Not circuits with no signal received on either input terminal produce a negative signal which is delivered to the set input terminal of a corresponding counter bit in the second counter to set that counter'bit to its one state. The number in the first counter has thusbeen transferred to the second couner. Each counter hit in the first counter having a one stored therein transferred that one to a correspond- "ing counter hit in the second counter in the manner described above. The counter bits remaining in their zero state correspond to a counter bit in the zero state in the first counter. Table 3 shows the number 5980 in the first counter and Table 4 the number 5980 after transfer to the second counter.

The second counter shown as block 18 in FIG. 1 is shown in more detail in FIGS. 2B and 2C and is composed of thirteen counter .bits 151-163. The second counter operates in a similar manner to the first counter except that the 0 terminal of each counter bit is connected to the input terminal of each succeeding counter hit and each pulse applied to the second counter causes a one to be subtracted from the number resting in the counter in a manner to be described.

The transfer of the number 5980 from thefirst counter ,to'the second counterhas been described and the number .5980 now rests in the, second counter in binary form as shown in Table 4. As the hot metal enters the rolls for the reverse run, gate 21 is conditioned to pass the pulses ,from the rate adjuster. The first pulse applied to the first counter hit 151 causes counter bits 151-154 to be set to one and counter bit 155 reset to zero. The 0 terminals of each counter bit are connected to the input terminal of the next succeeding counter bit; so that when counter hit 151 switches from the zero state to the one state, the negative signal from the 0 terminal goes positive to ground potential and causes counter bit 152 to switch the first counter hit 151 of the second counter causes 1o the number in the second counter to be reduced inthe manner described above and shown in Table 4.

INITIATION OF SLOWDOWN the tail end of the metal a different distance from the rolls for each speed. The motor and controls 14 notifies the speed indicator 22 which speed the hot metal is traveling and a negative level produced by the speed indicator on one of five output lines and applied to one of five And circuits -174. A digital tachometer plus an analog-to-digital converter would function as speed indicator 22 to indicate the speed of the metal as a function of the speed of the motor 14. A digital tachometer is discussed on pages 5-68 of Control Engineers Handbook, by Truxal, published in 195 8 by McGraw-Hill. On the same page of Truxal a suitable analog-to-digital converter is referred to as shown in FIG. 5.64(b'), on pages 5- 65 of the Control Engineers Handbook. And circuits 17 0- -174are conventional And circuitswhich produce an output signal upon receiving two negative input signals.

, The number resting in the second counter is representative of the length of the hot metal which has been rolled on the previous run; and after allowing for the compensating factor caused by the reduction in thickness and resulting increase in length, the number in the second counter also represents the length of the hot metal to be rolled.

The 1 terminals of the counter bits 157-161 are connected to a decoder 175. Decoder is a conventional decoder which decodes the binary inputs on five lines and produces an outputsignal on one line which is applied to one ofthe And circuits 170-175; 3 Decoder 175 decodes the signals from the counter bits on the negative going side of the signal when the 1' terminal goes from ground potential to a negative potential.

, The decoder 175 and the And circuits 170-174 together perform the comparison function of comparison circuit'23 in FIG.'1; Table 5 shows the necessary state ,of the counter bits toapply a signal from the decoder to ,a specific And circuit Table 5 also shows'rthe decimal number resting in the second counter which causes a signal to be applied to a specific And circuit. For instance, when the number in the second counter is stepped down to 127 of binary 1111111000000 with 10000 in the counter bits 157-161, a negative signal is produced by the 1 terminal-of counter bit 157 and the 1 terminals of counter bits 158-161 are at ground potential. The decoder 175 responds by delivering a signal to And'circuit 170. I

As stated, the number resting in the second counter representsthe length of the'hotmetal remaining to be rolled. The speed'indicator applies a signal to one of the And circuits indicating at what length slowdown is to be initiated. If the slowdown is to be initiated at a length represented by the number 127 resting in second counter, a signal is applied to And circuit 170. Thus, when second counter is stepped down to the number 127 as described, a signal is applied to And circuit 170 from the decoder 1 1' V 175 so that And circuit 170 produces a signal which is delivered to the slowdown control 26. The slowdown control 26 delivers a signal to the motor and controls 14 to initiate a slowdown of the hotmetal.

In the embodiment illustrated slowdown may be initiated as the second counter is steppeddown to the numbers 1087, 575, 319, 181, and 127. Signals must be applied to the appropriate And circuits from both the decoder 175 and the speed indicator 22 in the manner described and shown in Table 5 to initiate slowdown.

7 Table 6 Table 6 shows the states of all of the counter bits in the second counter as the number in the counter is reduced from 130 to 127.

The reset circuits 125, 126, and 127 are standard circuits which produce pulses to clear the pulse rate adjustor and the two counters at the desired time upon notification from the metal in rolls detector after the hot metal has left the rolls. Reset circuit 125 delays delivering the reset pulse to the first counter until the second counter has been cleared, and the number in the first counter transferred to the second counter.

The metal in rolls detector 15 is composed of a hot metal detector which detects the presence or absence of the hot metal between the rolls. After the hot metal leaves the rolls, the metal in rolls detector delivers a signal to the reverse circuit 16 to initiate a reverse operation and signals to the reset circuits to reset the counters and the pulse rate adjustor.

The reverse circuit 16 is a circuit which normally applies negative signals to the And-Not circuits; and when the hot metal leaves the rolls, removes the negative signal so the inputs to the And-Not circuits are at ground potential to transfer the number in the first counter to the second counter. The reverse circuit 16 also delivers a signal to the motor and controls 14 to reverse the direction of rotation of the rolls 11 and 13.

Motor and controls 14 are standard items known in "the art. The motor is mechanically linked to the rolls 11 and 13 to rotate those rolls. The rolls may be reversed by either reversing the motor or by mechanical linkage. Upon receiving a signal from the slowdown circuit 26, the rolls are slowed down by slowing down the motor or by adjusting the mechanical linkage in a well-known manner.

In summary a slowdown control for a reversing hot mill has been described. The slowdown control is economical and accurate. Slowdown may be initiated a different distance from the rolls for each speed at which the hot metal is traveling.

While this invention has been explained and described with the aid of a particular embodiment thereof, it will be understood that the invention is not limited thereby and that many modifications will occur to those skilled in the art. It is therefore contemplated by the appended claims to cover all such modifications as fall within the scope and spirit of the invention.

What is claimed is: V 1. Apparatus for determining the length of metal remaining to be rolled in a reversing hot metal mill comprising, means for measuring the length of metal traveling through the rolls of a hot mill in a first pass and storing a representation thereof, means for reducing said stored representation as the metal travels in a second pass, in accordance with the length of metal traveling 12 through the rolls in the second pass, and means for producing'an indication of the length of the metal remaining to be rolled in the second pass.

2. Apparatus for determining the length of metal remaining to be rolled in a reversing hot metal mill comprising, counter means, measuring means for measuring the length of metal traveling through the rolls of a hot mill in a first pass, means for causing a representation of the length of the metal which has traveled through the rolls to be transferred to said counter means after the metal has left the rolls, and means for causing said stored representation in said counter means to be reduced as the metal travels in a second pass through the rolls in accordance with the length of metal traveling through the rolls in the second pass, said counter means producing an indication of the length of the metal remaining to be rolled in the second pass.

3. A slowdown control for a reversing hot metal mill comprising counter means, measuring means for measuring the length of metal traveling through the rolls of a hot mill in a first pass, means for causing a representation of the length of the metal which has traveled through the rolls to be transferred to said counter means after the metal has left the rolls, means for causing said stored representation in said counter means to be reduced as the metal travels in a second pass through the rolls in accordance with the length of metal traveling through the rolls in the second pass, said counter means producing signals indicating the length of the metal remaining to be rolled in the second pass, speed indicating means for producing signals indicating the speed of travel of the metal, and comparison means for comparing the signals produced by said counter means, and said speed indicating means and when a predetermined relationship exists between said signals for producing a signal to initiate slowdown of said metal.

4. Apparatus for determining the length of metal re- .maining to be rolled in a reversing hot metal mill, comprising means for generating pulses in synchronism with the length of metal traveling through the rolls of a hot mill in a first pass, first counter means for counting said pulses as the metal travels through the rolls, second counter means,. means for causing the number accumulated in the first counter means to be transferred to to said second counter means after the metal leaves the rolls so that a number representing the length of the metal rolled in the first pass through the rolls rests in said second counter means, compensating means for causing the number resting in said second counter means to be reduced as the metal travels through the rolls in the second pass in accordance with the increase in length resulting from the decrease in thickness so that the number in said second counter means represents the length of metal remaining to be rolled in the second pass.

.ing said stored representation to be reduced as the metal travels in a second pass in accordance with the length of metal traveling through the rolls in the second pass and for producing signals indicating the length of the metal remaining to be rolled in the second pass, speed indicating means for producing signals indicating the speed of travel of the metal, and comparison means for comparing the signals produced by said reducing means and said speed indicating means and when a predetermined relationship exists between said signals for producing a signal to initiate slowdown of the metal.

6. A slowdown control for a reversing hot metal mill comprising means for generating pulses in synchronism with the length of metal traveling through the rolls of a hot mill in a first pass, first counter means for counting said pulses as the metal travels through the rolls, second counter means, means for causing the number accumulated in the first counter to be transferred to said second counter means after the metal leaves the rolls so that a number representing the length of the metal rolled in the first pass through the rolls rests in said second counter means, compensating means for causing the number resting in said second counter means to be reduced as the metal travels through the rolls in the second pass in accordance with the increase in length resulting from the decrease in thickness so that the number in said second counter means represents the length of metal remaining to be rolled in the second pass, said second counter producing signals indicating the length of metal remaining to be rolled in the second pass, speed indicating means for producing signals indicating the travel speed of the metal, and comparison means for comparing the signals produced by said second counter means and said speed indicating means and for producing a signal to initiate slowdown of the metal when a predetermined relationship exists between said signals.

7. Apparatus for determining the length of metal remaining to be rolled in a reversing hot metal mill, comprising means for generating pulses in synchronism with the length'of metal traveling through the rolls of a hot mill in a first pass, first counter means for counting said pulses as the metal travels through the rolls, second counter means, means for causing the number accumulated in the first counter means to be transferred to said second counter means after the metal leaves the rolls so that a number representing the length of the metal rolled in the first pass through the rolls rests in said second counter means, and pulse rate adjusting means responsive to the pulsesfrom said pulse generator for generating pulses at a compensated rate in accordance with the increased length of the metal being rolled in the second pass and applying such pulses to said second counter to reduce the number in said second counter as the metal travels through the rolls in the second pass so that the number in said second counter represents the length of metal remaining to be rolled in the second pass.

8. Apparatus for determining the length of metal remaining to be rolled in a reversing hot metal mill, comprising means for generating pulses in synchronism with the length of metal traveling through the rolls of a hot mill in a first pass, first counter means for counting said pulses as the metal travels through the rolls, second counter means, means for causing the number accumulated in the first counter means to be transferred to said second counter means after the metal leaves the rolls so that a number representing the length of the metal rolled in the first pass through the rolls rests in said second counter means, pulse rate adjusting means responsive to the pulses from said pulse generator for generating pulses at a compensated rate in accordance with the increased length of the metal being rolled in the second pass and applying such pulses to said second counter to reduce the number in said second counter as the metal travels through the rolls in the second pass so that the number in said second counter represents the length of metal remaining to be rolled in the second pass, said second counter producing signals indicating the length of metal remaining to be rolled in the second pass, speed indicating means for producing signals indicating the travel speed of the metal, and comparison means for comparing the signals produced by said counter means and said speed indicating means and-for producing a signal to initiate slowdown of the metal when a predetermined relationship exists between said signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,071,176 Pollok Feb. 16, 1937 2,214,617 Kenyon Sept. 10, 1940 2,322,080 Wickler et al. June 15, 1943 3,015,974 Orbon et al Jan. 9, 1962 

1. APPARATUS FOR DETERMINING THE LENGTH OF METAL REMAINING TO BE ROLLED IN A REVERSING HOT METAL MILL COMPRISING, MEANS FOR MEASURING THE LENGTH OF METAL TRAVELING THROUGH THE ROLLS OF A HOT MILL IN A FIRST PASS AND STORING A REPRESENTATION THEREOF, MEANS FOR REDUCING SAID STORED REPRESENTATION AS THE METAL TRAVELS IN A SECOND PASS, IN ACCORDANCE WITH THE LENGTH OF METAL TRAVELING THROUGH THE ROLLS IN THE SECOND PASS, AND MEANS FOR PRODUCING AN INDICATION OF THE LENGTH OF THE METAL REMAINING TO BE ROLLED IN THE SECOND PASS. 